Presence/absence of peritrophic membrane in the gut of shrimp without and with a peroral flush. Peritrophic membrane (PM) was stained with FITC-linked succinylated (WGA) wheat germ agglutinin and analyzed by fluorescence microscopy. Bar = 100 µm. The cell nuclei were stained by Hoechst. Photomicrographs 1–3 show the presence of PM in the midgut (segment S2 and S4) and hindgut lumen (segment S6) of control samples (without a peroral flush). Photomicrographs 4–6 show the absence of PM in the midgut and hindgut lumen of perorally flushed shrimp. FITC-linked succinylated WGA also labeled the basement membrane (BM) of the midgut (photomicrographs 1, 2, 4 and 5) and the cuticle that lined the hindgut lumen (CLH, photomicrographs 3 and 6).